1. Field of the Invention
The present invention relates to water-redispersible, storage-stable pulverulent compositions based on particulates of a water-insoluble vinyl and/or acrylic polymer. This invention also relates to the use of such powders, for example as a component of hydraulic binders for the construction industry.
2. Description of the Prior Art
Redispersible powders which are produced by spray drying dispersions of vinyl and/or acrylic polymers, especially dispersions of vinyl ester polymers, are known to this art.
To successfully produce powders which do not agglomerate during storage under the influence of pressure and of temperature and which are conveniently redispersible in water, large amounts of inert materials and of protective colloids are typically added thereto.
Vinyl and/or acrylic polymers are frequently used as adjuvants in hydraulic inorganic binder compositions to improve their intended applications and improve the properties of the material after hardening, such as adhesion to various substrates, impermeability, flexibility and mechanical properties. The redispersible powders have the advantage over aqueous dispersions that they can be premixed with the cement in the form of ready-to-use pulverulent compositions which may be employed, for example, for the manufacture of mortars and the concretes intended to be bonded to building materials, or for the manufacture of adhesive mortars, or for the production of protective coatings and decorative coatings for the inside or outside of buildings.
However, it is known to this art that the adhesion of the hardened coatings diminishes after exposure to a moist environment.
To prevent the agglomeration of redispersible powders of polymers without adversely affecting the adhesive properties thereof, it has been proposed to add to the dispersions, prior to spraying, melamine/formaldehyde/sulfonate condensation products (U.S. Pat. No. 3,784,648) or naphthalene/formaldehyde/sulfonate condensation products (DE-A-3,143,070) and/or vinylpyrrolidone/vinyl acetate copolymers (EP-78,449). These water-soluble compounds, however, do not provide improvement in respect of the aforesaid loss of adhesion in the moist state.